Israel's military warned Tuesday the Lebanese militia of Hezbollah against approaching the border fence, hours after it launched an operation to "expose and thwart" cross-border tunnels built by the group.

Israel Defense Forces (IDF) Spokesman in Arabic, Avichay Adraee, addressed Hezbollah militants and Lebanon's army soldiers, warning them against entering or getting near the tunnels.

"Your life is in danger, be warned," he wrote on Twitter.

The military issued a statement, saying that overnight between Monday and Tuesday, it had launched an operation, dubbed "Northern Shield," to "thwart and neutralize cross-border attack tunnels."

Head of the international media branch at the IDF's Spokesperson's Unit, Jonathan Conricus, told reporters during a phone briefing that this is "the first stage of the operation" in which the aim is "to expose and thwart" the tunnels.

Conricus said Israeli forces up north have been put on "heightened alert" but no reserve forces have been called up, and the area around the northern Israeli city of Metula, which is next to the Lebanese border, has been declared a closed military zone.

Israel and Hezbollah, an Iran-backed militia in southern Lebanon, had a month-long war in 2006 that ended in a ceasefire.